The present invention relates to bactericides, and more particularly, to bactericides that kill harmful microorganisms including those belonging to the genus Legionella.
Heat exchangers used in air-regulators, or the like, are generally provided with fins to exchange heat. The fins of a typical heat exchanger are exposed to ambient air to release heat into the air. A stream of air may be forced through the fins to facilitate the heat exchange between the fins and the air. Accordingly, the fins are subjected to moisture and dust particles present in the air. This provides a suitable environment for the growth of health-impairing microorganisms such as fungi or pathogenic bacteria including the genus Legionella.
Certain acidic or basic solutions, known as pH regulators, surfactants, organic solvents, or mixtures thereof have been used as cleansing agents for equipment, including heat exchanging fins, where microorganisms are likely to grow. Japanese Unexamined Publication No.8-157899 describes a spray-type cleaning agent for spraying washing agent foam onto surfaces of equipment to be cleansed. The foamed agent stays on the surface of the parts, e.g. fins, for an extended period of time.
Although it can effectively remove such deposits as scale or sediment, this cleaning agent is not capable of completely killing or removing microorganisms that grow on the surface of the fins. The use of the agent in a large amount can suppress the growth of microorganisms to some extent. Complete sanitization, however, can not be achieved with the agent due to its nature as a cleaner rather than a bactericide. Because of the agent's lack of bactericidal effect, microorganisms that have not been removed can readily proliferate. This may lead to clogging of the drainage pipe by plaque formed by bacteria, and subsequently, to an incomplete discharge of collected condensation water, which collects in a discharge pan.
Conventional sanitizing chemicals include strong oxidizing reagents such as hydrogen peroxide, sodium hypochlorite and calcium hypochlorite, as well as bactericides including glutaraldehyde, and strong acids including hydrochloric acid. Twenty-four hour hot tubs, which are often used in Japan, recirculate the same water repeatedly while the water is sanitized and purified with an integrated biological purification system. When applied to the bath system, the above-mentioned chemicals work non-selectively on a wide range of microorganisms, killing not only harmful bacteria such as Legionella but also favorable bacteria inhabiting the system. Consequently, the purifying effect of the system would be lost.
In addition, gas is produced when hydrogen peroxide and sodium hypochlorite are used in bactericidal application. The gas can cause a problem in the purification system in that the discharge chamber of the pump fills with the gas, and consequently the pump loses its prime. As a result, the water flow in the piping system is disrupted.
Sodium hypochlorite and calcium hypochlorite are highly corrosive to metal. Also, they may produce toxic gas when mixed with other reagents. These factors substantially restrict application of the reagents.
Strong acids such as hydrochloric acid are not suitable used for sanitizing purposes unless an anti-corrosive coating is applied to protect metal parts. Sanitization with strong acids, therefore, requires by certain restriction.